Abstract
Liquid–liquid extraction of mixture of seven heavy rare-earths (HREs) such as terbium, dysprosium, holmium, yttrium, erbium, ytterbium, and lutetium and mixture of four light rare-earths (LREs) such as lanthanum, cerium, praseodymium and neodymium has been investigated from phosphoric acid solutions. Extractants used are, Talcher organic phosphorus solvent (TOPS 99), an equivalent to di-2-ethylhexyl phosphoric acid, 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC-88A), and bis(2,4,4-trimethylpentyl) phosphinic acid (Cyanex 272). The objective of the present study was to investigate the extraction behavior and separation possibilities among HREs and LREs and also separation of HREs as a group from LREs in 3–5 M acid, which is similar to wet phosphoric acid concentration. The parameters studied include time, H 3PO 4 concentration and extractant concentration. The percent extraction of metal decreases as the acid concentration increases with any given extractant concentration. Mechanism of metal transfer follows ion exchange type. The separation factors were evaluated based on the distribution coefficients in order to estimate the potential of the results for the separation of individual/pair of rare-earths from others and the separation of HREs from LREs. Extraction efficiency of extractants towards lanthanides from H 3PO 4 medium decreases in the series: TOPS 99 > PC 88A > Cyanex 272.
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